Drainage of pulp is an important phenomenon operating during the papermaking process and in other situations where dewatering of pulp stocks is necessary. In most situations, it is necessary to characterize the dewaterability or drainability of pulp suspensions by using some measure. The principal purposes for which drainage testers have been used in the papermaking industry include: to evaluate pulp quality; to predict the paper machine drainage of a given furnish; to predict retention; and/or to predict pulp/paper physical properties such as strength and fiber flexibility.
The paper industry has traditionally sought a way to predict how changes in fiber (source and variation), refining, chemical additives and wet end conditions will effect the drainage of the papermaking furnish. The papermaking process is, in total, based on the separation of large quantities of water from fiber dispersed as a very dilute suspension. Thus, this knowledge would allow both the optimization of the dewatering process and a means of avoiding possible catastrophic upsets in the wet end system due to changes in the furnish components.
The importance of understanding the dewatering process has lead to the development of a number of devices to test, predict and monitor the drainage/dewatering process. These drainage testers usually rely on (a) measurement of drainage volume with time, (b) determination of specific filtration resistance, (c) determination of time to drain a certain volume under specific conditions, or (d) volume of water drained under specific conditions in a given time (see Unbehend, J. "A Critical Review of Drainage Testers," TAPPI Papermakers Conference (1991)). The following drainage testers are described in the literature:
1. Freeness testers (Canadian Standard Freeness, Schopper-Reigler)--see: "Drainage Time of Pulp," TAPPI Test Methods T221 su-72, TAPPI Atlanta Ga., (1996); El-Hosseiny, F. and J. F. Yan, "Mathematic Models for Freeness" Pulp Paper Mag., Can 81, 6, 61, (1980); and Swodzinski, P. C. and M. R. Doshi, "Mathematic Models of CSF and SR" TAPPI Intl. Process and Materials Quality Evaluation Conf. Proceedings, 253 (1986). PA1 2. Dynamic drainage jar--see Penniman, J. G. and C. R. Olson, "Using the Britt Jar to Measure the Drainage" Paper Trade J., 34-36 (April 1979). PA1 3. Turbulent sheet forming device--see Britt, K. W., J. Unbehend and R. Shridharan, "Observations on Water Removal on Papermaking" TAPPI 69, 7, 76-79 (1986). PA1 4. Vacuum water release analyzer--see Britt, K. W., J. Unbehend and R.Shridharan, "Observations on Water Removal in Papermaking" TAPPI 69, 7, 76-79 (1986). PA1 5. Specific filtration resistance tester see Pires, E. C., A. M. Springer, V. Kumar "A New Technique for Specific Filtration Resistance Measurement" TAPPI J., 149-153 (July 1989). PA1 6. G/W drainage system--see Gess, J. M. "An Introduction to the G/W Drainage Retention System." TAPPI Short Course Notes on Retention and Drainage, 49-52 (1989). PA1 7. Determination of beating degree--see Alfthan, G. V. "A Sensitive Apparatus for Rapid Determination of Beating Degree." Paper Ochtra, 6-7 (1976). PA1 8. A tester based on constant rate rapid drainage--see Andrews, B. D. and L. R. White "A Constant Rate Rapid Drainage Tester." TAPPI J., 52, 6, 1171-1175 (1969). PA1 9. Nisser's openness tester--see Nisser, H, "Determination of the Filterability of Cellulose Fiber Suspensions" Transl. from Swedish, Pulp and Paper Research Institute of Canada, Series No. 313 (1978). PA1 10. The moving belt drainage tester--see Karrila, S., K. Raisanen and H. Paulopuro, TAPPI Papermakers' Conf. Proceedings, 275 (1992).
Notwithstanding the wide range of drainage testers described in the literature, as represented by the above-summarized techniques, all current testers and test methodologies suffer from two main disadvantages. First, the existing measurements are used in an empirical manner. Conventionally, the drainability measure or index represents some physical quantity which is monitored under a very specific experimental configuration and under very specific external physical conditions. The empiricism of these measurements means that they cannot be easily extrapolated to different conditions of pulp consistency, pressure or configurations. Secondly, although some of the measures purport to measure a more fundamental quantity for the pulps like the specific filtration resistance, they do so only under very specific conditions. These also suffer from the problem of not being true fundamental pulp properties and hence are not entirely useful for predictive or control purposes.
In other words, the parameters determined by the above-named testers are not fundamental parameters of a paper pulp. Whether it is the freeness (CSF or SR) or the time of drainage in a DDJ or the time taken under different vacuum conditions (turbulent sheet forming device or vacuum water release analyzer) or the specific filtration resistance tester, they each measure the properties of a pulp under a certain unique configuration. Therefore, extending the test results to a new situation or interpretation of the test results in terms of a pulp property is rendered difficult. The present invention addresses this difficulty by providing a new tester and testing methodology to determine the true characteristics of a papermaking pulp suspension. These characteristics may then be used to control various pulp processing operations.